/* @(#)s_erf.c 5.1 93/09/24 */
/*
* ================================================== ==
* Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
*
* Developed at SunPro, a Sun Microsystems, Inc. business.
* Permission to use, copy, modify, and distribute this
* software is freely granted, provided that this notice
* is preserved.
* ================================================== ==
*/

/* double erf(double x)
* double erfc(double x)
* x
* 2 |\
* erf(x) = --------- | exp(-t*t)dt
* sqrt(pi) \|
* 0
*
* erfc(x) = 1-erf(x)
* Note that
* erf(-x) = -erf(x)
* erfc(-x) = 2 - erfc(x)
*
* Method:
* 1. For |x| in [0, 0.84375]
* erf(x) = x + x*R(x^2)
* erfc(x) = 1 - erf(x) if x in [-.84375,0.25]
* = 0.5 + ((0.5-x)-x*R) if x in [0.25,0.84375]
* where R = P/Q where P is an odd poly of degree 8 and
* Q is an odd poly of degree 10.
* -57.90
* | R - (erf(x)-x)/x | <= 2
*
*
* Remark. The formula is derived by noting
* erf(x) = (2/sqrt(pi))*(x - x^3/3 + x^5/10 - x^7/42 + ....)
* and that
* 2/sqrt(pi) = 1.128379167095512573896158903121545171688
* is close to one. The interval is chosen because the fix
* point of erf(x) is near 0.6174 (i.e., erf(x)=x when x is
* near 0.6174), and by some experiment, 0.84375 is chosen to
* guarantee the error is less than one ulp for erf.
*
* 2. For |x| in [0.84375,1.25], let s = |x| - 1, and
* c = 0.84506291151 rounded to single (24 bits)
* erf(x) = sign(x) * (c + P1(s)/Q1(s))
* erfc(x) = (1-c) - P1(s)/Q1(s) if x > 0
* 1+(c+P1(s)/Q1(s)) if x < 0
* |P1/Q1 - (erf(|x|)-c)| <= 2**-59.06
* Remark: here we use the taylor series expansion at x=1.
* erf(1+s) = erf(1) + s*Poly(s)
* = 0.845.. + P1(s)/Q1(s)
* That is, we use rational approximation to approximate
* erf(1+s) - (c = (single)0.84506291151)
* Note that |P1/Q1|< 0.078 for x in [0.84375,1.25]
* where
* P1(s) = degree 6 poly in s
* Q1(s) = degree 6 poly in s
*
* 3. For x in [1.25,1/0.35(~2.857143)],
* erfc(x) = (1/x)*exp(-x*x-0.5625+R1/S1)
* erf(x) = 1 - erfc(x)
* where
* R1(z) = degree 7 poly in z, (z=1/x^2)
* S1(z) = degree 8 poly in z
*
* 4. For x in [1/0.35,28]
* erfc(x) = (1/x)*exp(-x*x-0.5625+R2/S2) if x > 0
* = 2.0 - (1/x)*exp(-x*x-0.5625+R2/S2) if -6<x<0
* = 2.0 - tiny (if x <= -6)
* erf(x) = sign(x)*(1.0 - erfc(x)) if x < 6, else
* erf(x) = sign(x)*(1.0 - tiny)
* where
* R2(z) = degree 6 poly in z, (z=1/x^2)
* S2(z) = degree 7 poly in z
*
* Note1:
* To compute exp(-x*x-0.5625+R/S), let s be a single
* precision number and s := x; then
* -x*x = -s*s + (s-x)*(s+x)
* exp(-x*x-0.5626+R/S) =
* exp(-s*s-0.5625)*exp((s-x)*(s+x)+R/S);
* Note2:
* Here 4 and 5 make use of the asymptotic series
* exp(-x*x)
* erfc(x) ~ ---------- * ( 1 + Poly(1/x^2) )
* x*sqrt(pi)
* We use rational approximation to approximate
* g(s)=f(1/x^2) = log(erfc(x)*x) - x*x + 0.5625
* Here is the error bound for R1/S1 and R2/S2
* |R1/S1 - f(x)| < 2**(-62.57)
* |R2/S2 - f(x)| < 2**(-61.52)
*
* 5. For inf > x >= 28
* erf(x) = sign(x) *(1 - tiny) (raise inexact)
* erfc(x) = tiny*tiny (raise underflow) if x > 0
* = 2 - tiny if x<0
*
* 7. Special case:
* erf(0) = 0, erf(inf) = 1, erf(-inf) = -1,
* erfc(0) = 1, erfc(inf) = 0, erfc(-inf) = 2,
* erfc/erf(NaN) is NaN
*/
static const double tiny = 1e-300,
	half= 5.00000000000000000000e-01, /* 0x3FE00000, 0x00000000 */
	one = 1.00000000000000000000e+00, /* 0x3FF00000, 0x00000000 */
	two = 2.00000000000000000000e+00, /* 0x40000000, 0x00000000 */
	/* c = (float)0.84506291151 */
	erx = 8.45062911510467529297e-01, /* 0x3FEB0AC1, 0x60000000 */
	/*
	* Coefficients for approximation to erf on [0,0.84375]
	*/
	efx = 1.28379167095512586316e-01, /* 0x3FC06EBA, 0x8214DB69 */
	efx8= 1.02703333676410069053e+00, /* 0x3FF06EBA, 0x8214DB69 */
	pp0 = 1.28379167095512558561e-01, /* 0x3FC06EBA, 0x8214DB68 */
	pp1 = -3.25042107247001499370e-01, /* 0xBFD4CD7D, 0x691CB913 */
	pp2 = -2.84817495755985104766e-02, /* 0xBF9D2A51, 0xDBD7194F */
	pp3 = -5.77027029648944159157e-03, /* 0xBF77A291, 0x236668E4 */
	pp4 = -2.37630166566501626084e-05, /* 0xBEF8EAD6, 0x120016AC */
	qq1 = 3.97917223959155352819e-01, /* 0x3FD97779, 0xCDDADC09 */
	qq2 = 6.50222499887672944485e-02, /* 0x3FB0A54C, 0x5536CEBA */
	qq3 = 5.08130628187576562776e-03, /* 0x3F74D022, 0xC4D36B0F */
	qq4 = 1.32494738004321644526e-04, /* 0x3F215DC9, 0x221C1A10 */
	qq5 = -3.96022827877536812320e-06, /* 0xBED09C43, 0x42A26120 */
	/*
	* Coefficients for approximation to erf in [0.84375,1.25]
	*/
	pa0 = -2.36211856075265944077e-03, /* 0xBF6359B8, 0xBEF77538 */
	pa1 = 4.14856118683748331666e-01, /* 0x3FDA8D00, 0xAD92B34D */
	pa2 = -3.72207876035701323847e-01, /* 0xBFD7D240, 0xFBB8C3F1 */
	pa3 = 3.18346619901161753674e-01, /* 0x3FD45FCA, 0x805120E4 */
	pa4 = -1.10894694282396677476e-01, /* 0xBFBC6398, 0x3D3E28EC */
	pa5 = 3.54783043256182359371e-02, /* 0x3FA22A36, 0x599795EB */
	pa6 = -2.16637559486879084300e-03, /* 0xBF61BF38, 0x0A96073F */
	qa1 = 1.06420880400844228286e-01, /* 0x3FBB3E66, 0x18EEE323 */
	qa2 = 5.40397917702171048937e-01, /* 0x3FE14AF0, 0x92EB6F33 */
	qa3 = 7.18286544141962662868e-02, /* 0x3FB2635C, 0xD99FE9A7 */
	qa4 = 1.26171219808761642112e-01, /* 0x3FC02660, 0xE763351F */
	qa5 = 1.36370839120290507362e-02, /* 0x3F8BEDC2, 0x6B51DD1C */
	qa6 = 1.19844998467991074170e-02, /* 0x3F888B54, 0x5735151D */
	/*
	* Coefficients for approximation to erfc in [1.25,1/0.35]
	*/
	ra0 = -9.86494403484714822705e-03, /* 0xBF843412, 0x600D6435 */
	ra1 = -6.93858572707181764372e-01, /* 0xBFE63416, 0xE4BA7360 */
	ra2 = -1.05586262253232909814e+01, /* 0xC0251E04, 0x41B0E726 */
	ra3 = -6.23753324503260060396e+01, /* 0xC04F300A, 0xE4CBA38D */
	ra4 = -1.62396669462573470355e+02, /* 0xC0644CB1, 0x84282266 */
	ra5 = -1.84605092906711035994e+02, /* 0xC067135C, 0xEBCCABB2 */
	ra6 = -8.12874355063065934246e+01, /* 0xC0545265, 0x57E4D2F2 */
	ra7 = -9.81432934416914548592e+00, /* 0xC023A0EF, 0xC69AC25C */
	sa1 = 1.96512716674392571292e+01, /* 0x4033A6B9, 0xBD707687 */
	sa2 = 1.37657754143519042600e+02, /* 0x4061350C, 0x526AE721 */
	sa3 = 4.34565877475229228821e+02, /* 0x407B290D, 0xD58A1A71 */
	sa4 = 6.45387271733267880336e+02, /* 0x40842B19, 0x21EC2868 */
	sa5 = 4.29008140027567833386e+02, /* 0x407AD021, 0x57700314 */
	sa6 = 1.08635005541779435134e+02, /* 0x405B28A3, 0xEE48AE2C */
	sa7 = 6.57024977031928170135e+00, /* 0x401A47EF, 0x8E484A93 */
	sa8 = -6.04244152148580987438e-02, /* 0xBFAEEFF2, 0xEE749A62 */
	/*
	* Coefficients for approximation to erfc in [1/.35,28]
	*/
	rb0 = -9.86494292470009928597e-03, /* 0xBF843412, 0x39E86F4A */
	rb1 = -7.99283237680523006574e-01, /* 0xBFE993BA, 0x70C285DE */
	rb2 = -1.77579549177547519889e+01, /* 0xC031C209, 0x555F995A */
	rb3 = -1.60636384855821916062e+02, /* 0xC064145D, 0x43C5ED98 */
	rb4 = -6.37566443368389627722e+02, /* 0xC083EC88, 0x1375F228 */
	rb5 = -1.02509513161107724954e+03, /* 0xC0900461, 0x6A2E5992 */
	rb6 = -4.83519191608651397019e+02, /* 0xC07E384E, 0x9BDC383F */
	sb1 = 3.03380607434824582924e+01, /* 0x403E568B, 0x261D5190 */
	sb2 = 3.25792512996573918826e+02, /* 0x40745CAE, 0x221B9F0A */
	sb3 = 1.53672958608443695994e+03, /* 0x409802EB, 0x189D5118 */
	sb4 = 3.19985821950859553908e+03, /* 0x40A8FFB7, 0x688C246A */
	sb5 = 2.55305040643316442583e+03, /* 0x40A3F219, 0xCEDF3BE6 */
	sb6 = 4.74528541206955367215e+02, /* 0x407DA874, 0xE79FE763 */
	sb7 = -2.24409524465858183362e+01; /* 0xC03670E2, 0x42712D62 */

extern double exp(double);
extern double fabs(double);
double erf(double x)
{
	int n0,hx,ix,i;
	double R,S,P,Q,s,y,z,r;
	n0 = ((*(int*)&one)>>29)^1;
	hx = *(n0+(int*)&x);
	ix = hx&0x7fffffff;
	if(ix>=0x7ff00000) { /* erf(nan)=nan */
		i = ((unsigned)hx>>31)<<1;
		return (double)(1-i)+one/x; /* erf(+-inf)=+-1 */
	}

	if(ix < 0x3feb0000) { /* |x|<0.84375 */
		if(ix < 0x3e300000) { /* |x|<2**-28 */
			if (ix < 0x00800000)
				return 0.125*(8.0*x+efx8*x); /*avoid underflow */
			return x + efx*x;
		}
		z = x*x;
		r = pp0+z*(pp1+z*(pp2+z*(pp3+z*pp4)));
		s = one+z*(qq1+z*(qq2+z*(qq3+z*(qq4+z*qq5))));
		y = r/s;
		return x + x*y;
	}
	if(ix < 0x3ff40000) { /* 0.84375 <= |x| < 1.25 */
		s = fabs(x)-one;
		P = pa0+s*(pa1+s*(pa2+s*(pa3+s*(pa4+s*(pa5+s*pa6)))));
		Q = one+s*(qa1+s*(qa2+s*(qa3+s*(qa4+s*(qa5+s*qa6)))));
		if(hx>=0) return erx + P/Q; else return -erx - P/Q;
	}
	if (ix >= 0x40180000) { /* inf>|x|>=6 */
		if(hx>=0) return one-tiny; else return tiny-one;
	}
	x = fabs(x);
	s = one/(x*x);
	if(ix< 0x4006DB6E) { /* |x| < 1/0.35 */
		R=ra0+s*(ra1+s*(ra2+s*(ra3+s*(ra4+s*(
			ra5+s*(ra6+s*ra7))))));
		S=one+s*(sa1+s*(sa2+s*(sa3+s*(sa4+s*(
			sa5+s*(sa6+s*(sa7+s*sa8)))))));
	} else { /* |x| >= 1/0.35 */
		R=rb0+s*(rb1+s*(rb2+s*(rb3+s*(rb4+s*(
			rb5+s*rb6)))));
		S=one+s*(sb1+s*(sb2+s*(sb3+s*(sb4+s*(
			sb5+s*(sb6+s*sb7))))));
	}
	z = x;
	*(1-n0+(int*)&z) = 0;
	r = exp(-z*z-0.5625)*exp((z-x)*(z+x)+R/S);
	if(hx>=0) return one-r/x; else return r/x-one;
}

double erfc(double x)
{
	int n0,hx,ix;
	double R,S,P,Q,s,y,z,r;
	n0 = ((*(int*)&one)>>29)^1;
	hx = *(n0+(int*)&x);
	ix = hx&0x7fffffff;
	if(ix>=0x7ff00000) { /* erfc(nan)=nan */
		/* erfc(+-inf)=0,2 */
		return (double)(((unsigned)hx>>31)<<1)+one/x;
	}

	if(ix < 0x3feb0000) { /* |x|<0.84375 */
		if(ix < 0x3c700000) /* |x|<2**-56 */
			return one-x;
		z = x*x;
		r = pp0+z*(pp1+z*(pp2+z*(pp3+z*pp4)));
		s = one+z*(qq1+z*(qq2+z*(qq3+z*(qq4+z*qq5))));
		y = r/s;
		if(hx < 0x3fd00000) { /* x<1/4 */
			return one-(x+x*y);
		} else {
			r = x*y;
			r += (x-half);
			return half - r ;
		}
	}
	if(ix < 0x3ff40000) { /* 0.84375 <= |x| < 1.25 */
		s = fabs(x)-one;
		P = pa0+s*(pa1+s*(pa2+s*(pa3+s*(pa4+s*(pa5+s*pa6)))));
		Q = one+s*(qa1+s*(qa2+s*(qa3+s*(qa4+s*(qa5+s*qa6)))));
		if(hx>=0) {
			z = one-erx; return z - P/Q;
		} else {
			z = erx+P/Q; return one+z;
		}
	}
	if (ix < 0x403c0000) { /* |x|<28 */
		x = fabs(x);
		s = one/(x*x);
		if(ix< 0x4006DB6D) { /* |x| < 1/.35 ~ 2.857143*/
			R=ra0+s*(ra1+s*(ra2+s*(ra3+s*(ra4+s*(
				ra5+s*(ra6+s*ra7))))));
			S=one+s*(sa1+s*(sa2+s*(sa3+s*(sa4+s*(
				sa5+s*(sa6+s*(sa7+s*sa8)))))));
		} else { /* |x| >= 1/.35 ~ 2.857143 */
			if(hx<0&&ix>=0x40180000) return two-tiny;/* x < -6 */
			R=rb0+s*(rb1+s*(rb2+s*(rb3+s*(rb4+s*(
				rb5+s*rb6)))));
			S=one+s*(sb1+s*(sb2+s*(sb3+s*(sb4+s*(
				sb5+s*(sb6+s*sb7))))));
		}
		z = x;
		*(1-n0+(int*)&z) = 0;
		r = exp(-z*z-0.5625)*
			exp((z-x)*(z+x)+R/S);
		if(hx>0) return r/x; else return two-r/x;
	} else {
		if(hx>0) return tiny*tiny; else return two-tiny;
	}
}